The Quaternary Research (Daiyonki-Kenkyu)

Article

Early Holocene coseismic uplift and tsunami deposits recorded in a drowned valley deposit on the SE coast of the Boso Peninsula, central Japan

Osamu Fujiwara, Takanobu Kamataki, Jun-ichi Uchida, Kohei Abe, Tsuyosh ...

2009 Volume 48 Issue 1 Pages 1-10
Published: February 01, 2009
Released on J-STAGE: March 27, 2012

DOIhttps://doi.org/10.4116/jaqua.48.1

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This paper discusses a coseismic uplift which occurred around 8,200 cal BP along the southeast Boso Peninsula on the Pacific coast of central Japan facing the Japan Trench and Sagami Trough. Estimated uplift is based on eleven ¹⁴C ages and analyses of sedimentary facies, fossil assemblages of foraminifera and mollusks from the outcrops along the Onjaku River. The deposit is represented by alternation of mud, sand, and gravel beds deposited in a drowned valley system.
The results suggest that the relative sea-level rapidly fell around 8,200 cal BP. This phenomenon is discordant with the relative sea-level curve obtained from the Tokyo Bay area of small tectonic movements, which indicates a continuous relative sea-level rise toward a peak around 7,000 cal BP. Relative sea-level fall estimated from the study area probably reflected a local tectonic uplift.
Sand and gravel beds alternating with mud beds might be deposited by storm surges, river floods, and/or tsunamis that intruded into the muddy drowned valley. The conglomerate bed deposited just before the relative sea-level fall around 8,200 cal BP is interpreted as a tsunami deposit caused by the same earthquake that uplifted the study area.

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Short Article

The latest event at the eastern part of the Atotsugawa fault, inferred from the outcrops at Sako, Hida City, central Japan

Ryosuke Doke, Akira Takeuchi

2009 Volume 48 Issue 1 Pages 11-17
Published: February 01, 2009
Released on J-STAGE: March 27, 2012

DOIhttps://doi.org/10.4116/jaqua.48.11

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We discovered two fault outcrops at the eastern part of the Atotsugawa fault in Sako, Hida City. Radiocarbon dating of the samples from the fluvial strata of the outcrops indicates 100±30 yrs BP and 140±30 yrs BP. Since the fault plane clearly cut the strata, the latest faulting event occurred after these ages. This event is correlative with the AD1858 Hietsu earthquake, on the basis of the historical record of earthquakes in Japan. From the results of previous studies and this study, it is considered that the faulting occurred in all the section of the Atotsugawa fault during the latest event.
Because the timing and interval of the faulting events which occurred less than 10,000 years ago are almost compatible between the western and eastern parts of the Atotsugawa fault, it is probable that the older faulting events also occurred at once in all the parts of the fault.

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Report on International Union for Quaternary Research, XVII International Congress, July 28 to August 3, 2007, Cairns Convention Center, Queensland, Australia

Yoshiki Saito, Koji Okumura, Hisao Kumai

2009 Volume 48 Issue 1 Pages 19-44
Published: February 01, 2009
Released on J-STAGE: April 28, 2012

DOIhttps://doi.org/10.4116/jaqua.48.19

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